1. Field of the Invention
The present invention relates to a disc player of the recording type, and more particularly the invention relates to a disc player capable of improving an information recording accuracy in recording information in a disc-like optical recording medium of the erasable type.
2. Description of the Related Art
With progress of multimedia technology, the technical field of image processing calls for recording media capable of storing a large amount of digitized image data. A variety of information recording media are known. Of those recording media, inter alia an optical recording medium has attracted great attention with expectancy of superseding the magnetic tape because the optical recording medium has the following excellent features: capability of handling a large amount of digital information, ease of stopping dynamic image information and feeding of image frames, and random-access being possible.
Of the optical recording media, a CD-R (CD-recordable) is widely used which is categorized into the write-once optical recording media. A CD-RAM (CD-rewritable), which is categorized into an optical recording medium of the rewritable type, has been put in practical use.
The principles of the optical recording medium follow. Laser light is emitted from an optical pickup device toward the recording surface of the optical recording medium, and condensed and converted from optical energy to thermal energy, and the physical state of the recording surface of the optical recording medium is changed, with the thermal energy, to record information in the form of changes of the physical state.
It is frequent that the recording characteristics of the optical recording media are different for each disc even if those media are made of the same information storing material. This is due to the fact that the material properties and molding conditions are minutely different for each recording medium at the stage of their manufacturing. Therefore, even if a light beam is projected, at an optimum irradiation beam intensity, to the optical disc, information is not always recorded at the optimum irradiation beam intensity. In this state, it is difficult to secure a good uniformity of the accuracies of recording information into and reading out it from the optical recording medium.
To cope with this, a disc player for recording information into and reproducing it from the optical recording medium of this type, performs an optimum power calibration (OPC) for setting an irradiation intensity of a laser beam at an optimum value before starting an information recording operation.
The CD-R, for example, is provided with a power calibration area (PCA) 4 as shown in FIG. 7(a). The power calibration area 4 is located between a center hole 2 of an optical recording medium 1 and an information recording area 3. More precisely, it is located on the outer peripheral side of the center hole 2 and within the innermost periphery of the information recording area 3. Before information is recorded into the information recording area 3, test data is recorded into the power calibration area 4 of the recording medium, and an optimum disc irradiation beam intensity is determined on the basis of the recording test.
The OPC effectively operates when it is applied to such an optical recording medium 1 which ensures an optimum recording of information thereinto even when information is recorded into the entire recording area 3 of a disc-like optical recording medium 1 with a laser beam being fixed at an optimum disc irradiation beam intensity. In this case, an intensity of the laser beam, which is different from an optimum power determined by the recording test, which is applied to the power calibration area 4, is required for the optimum recording of information into the power calibration area 4 in the following cases. A first case is that the optimum disc irradiation beam intensity gradually increases from the inner side to the outer side (when viewed in the radial direction) of the recording area 3 of an optical recording medium 1 since a recording sensitivity is not uniform over the recording area 3 (as indicated by a straight line upwardly obliquely extending to the right in FIG. 7(b)). A second case is that the disc player, while being in power-on state, is left for a long time, and temperature in the disc player rises, the characteristic (I-P characteristic) of the laser diode varies, and the irradiation intensity of the laser beam is reduced (as indicated by a straight line downwardly obliquely extending to the right).
In the first case, an irradiation intensity of the laser beam required in the outer region (when radially viewed) of the optical recording medium 1 is larger than that in the inner region thereof.
When the laser beam of a fixed irradiation intensity, which is determined on the basis of the result of the recording test performed by use of the power calibration area 4 of the optical recording medium 1, is used for recording information into the entire recording area 3 of the optical recording medium 1, the light intensity of the laser beam becomes insufficient toward the outer side of the recording medium. Therefore, the information recording accuracy becomes deteriorated toward the outer side of the recording medium.
In the case of the phase-change type recording medium, such as a CD-RW, the rewriting of information into the recording medium is impossible. Further, the recording medium is limited in its power calibration range, so that the number of test recording operations is limited. As a result, an inconvenient situation occurs in which a testable area runs out in the power calibration area in a state that the information recordable area is still left in the recording area 3. In this situation, no recording test can be performed, and the information recording at an improper irradiation intensity of the light beam is inevitable.
Accordingly, an object of the present invention is to provide a disc player which is capable of recording information in the entire recording area of a disc-like optical recording medium at an optimum irradiation intensity of the laser beam, thereby improving an information recording accuracy.
According to the present invention, there is provided a disc player having laser output control means which controls a laser output power of a laser device at the time of actually recording information in a disc-like optical recording medium, in accordance with light being reflected from the recording medium in a recording test mode. The disc player is improved such that recording test is performed during a recording stand-by time period, which is yielded by a difference between an information transmittal rate in inputting information to the disc player and an information recording rate in recording information into the optical recording medium ((claim 1).
In the thus constructed disc player, the optical recording medium is a rewritable optical disc having rewriting capabilities, and the recording test is performed by use of a recording area of the optical recording medium into which information is recorded (claim 2).
In the disc player, the recording test is conducted by use of a recording area of one recording unit into which information is recorded (claim 3).
The disc player of the invention performs a recording test by the utilization of a stand-by period yielded by a difference between the data rate in inputting information to the disc player and a recording rate in recording information into the optical recording medium. The laser output control means an irradiation intensity of a laser beam for actually recording information on the basis of the result of the recording test. By the beam power control, an optimum recording of information over the entire information recording area of the optical recording medium is secured.
The optical recording medium used for the disc player is of the rewritable type. Therefore, information may be rewritten into the recording surface of the optical recording medium which contains information already recorded therein. The recording test is performed by use of the recording area into which information is recorded. Because of this, there is no limit in the number of test recording operations. Further, the recording test is performed by use of the recording area of one recording unit. Therefore, there is no chance that the test recording adversely affects the adjacent recording areas.